Animals, including humans, harbor a multitude of microbes (collectively referred to as the microbiota) in anatomical locations including the mouth, esophagus, stomach, small intestine, large intestine, caecum, vagina, skin, nasal cavities, ear, and lungs. The human microbiota is responsible for a multitude of critical processes, including the development of the immune system, metabolism of carbohydrates, proteins and xenobiotics, formation and regeneration of the epithelium, fat storage, production of hormones, production of vitamins, and protection from pathogen infections, among others (See e.g., LeBlanc et al. Curr. Opin. Biotechnol. (2013) 24(2):160-168; Hooper et al. Science (2012) 336(60801268-1273; Hughes et al. Am. J. Gastroenterol. (2013) 108(7):1066-1074). Modification of the human microbiota, which can be caused by a number of factors such as antibiotic use, excessive hygiene, diet, genetic background or combinations of the above, has been associated with a number of unwanted effects including the occurrence of infectious diseases (e.g., C. difficile infections), inflammatory, autoimmune and allergic diseases (e.g., ulcerative colitis, Crohn's disease, Type I diabetes, food allergies, asthma, rheumatoid arthritis) and metabolic diseases (e.g., Type II diabetes, metabolic syndrome, obesity, malnutrition), and cancer, among others. For instance, modifications of the microbiota can lead to a loss of tolerance against harmless food antigens or commensal bacterial antigens, subsequent excessive inflammatory responses, metabolic dysregulation, and damage to the intestinal tissue, which compromises its ability to serve as a barrier between the gut lumen and the systemic circulation.
Manipulation of the immune response is of great importance in the treatment of cancer and in vaccination. Cancer therapies that target the immune system have attained improvements in survival rates. However, a large percentage of patients do not respond to cancer immunotherapies. Similarly, large population subsets (e.g., the elderly) cannot mount strong immune responses to vaccines.
Approaches for countering the harmful effects of microbiota modifications on health are limited, despite the role that such modifications play in promoting human pathology. Interventions known to modulate the microbiota include antibiotics, prebiotics, probiotics and fecal transplants, each of which has limitations and potential adverse effects. Additional approaches to counter the detrimental effects of microbiome modification on human health are clearly needed. Furthermore, approaches for promoting stronger immune responses to cancer and to vaccines are also needed.